As internal combustion engines of the system whereby fuel is injected inside a cylinder--such engines generally called, for example, in-cylinder injection internal combustion engines or direct-injection internal combustion engines (DI internal combustion engines)--diesel engines are widely known. In spark ignition engines (hereinafter called "gasoline engines", as they are gasoline engines in general), those of the in-cylinder injection type have been proposed in recent years.
In such in-cylinder injection internal combustion engines, with a view to improving performance of the engines and reducing exhaust gas, there is a tendency toward increasing a fuel injection pressure to make fuel mist finer and hence to shorten a fuel injecting duration. Further, for engines equipped with supercharging systems, a high fuel injection pressure corresponding to a supercharging pressure is required during supercharging.
A fuel feeding system in an in-cylinder injection internal combustion engine is therefore constructed to feed fuel to a fuel injection valve by further pressurizing fuel through a high-pressure fuel pump subsequent to its pressurization through a low-pressure fuel pump so that such a sufficiently-high fuel injection pressure (for example, of several tens of atmospheres) can be obtained.
As a high-pressure fuel pump, however, a fuel pump of the engine-driven type is generally adopted. Its delivery pressure therefore corresponds to an engine speed (the number of revolutions of an engine). At the time of start-up of an engine, the number of revolutions of the engine is hence small so that the high-pressure fuel pump has an extremely low delivery pressure. The high-pressure fuel pump between a low-pressure fuel pump and a fuel injection valve conversely interferes with a flow of fuel, and a fuel pressure at the fuel injection valve fails to reach even a delivery pressure level of the low-pressure fuel pump.
Further, after the initiation of a start-up operation of the engine, the number of revolutions of the engine is generally low and the delivery pressure of the high-pressure fuel pump is low. The fuel is therefore at a low pressure level. A controller accordingly actuates the fuel injection valve in a low pressure mode. Upon elapse of a predetermined time after the initiation of a start-up operation of the engine, the number of revolutions of the engine generally increases, the delivery pressure of the high-pressure fuel pump becomes higher, and the fuel is brought to a high pressure level. The controller therefore actuates the fuel injection valve in a high pressure mode.
However, depending on the state or environment of the engine, for example, upon attempting a start-up at an extremely low temperature, the number of revolutions of the engine may not increase even when the predetermined time has elapsed. In contrast, the number of revolutions of the engine may increase even before the predetermined time elapses. A disharmony therefore arises between a fuel pressure and a control mode (low pressure mode or high pressure mode) of the fuel injection valve by the controller. As a result, an adequate fuel injection cannot be performed, thereby making it difficult to maintain stable combustion.
With a view to making it possible to obtain a predetermined fuel pressure even when the delivery pressure of a high-pressure fuel pump is not sufficient as in a start-up of an internal combustion engine and, further, to enable good combustion performance in the engine in accordance with a fuel pressure, a fuel feeding system for an internal combustion engine such as that shown in FIG. 5 has therefore been proposed, for example, in Japanese Patent Application Laid-Open (Kokai) No. HEI 7-83134 or the like.
In FIG. 5, there are shown fuel injection valves (injectors) 1, a fuel tank 2, a fuel line 3 arranged between the fuel injection valves 1 and the fuel tank 2, a low-pressure fuel pump 4 arranged in the fuel line 3 at an upstream location on a side of the fuel tank 2, and a high-pressure fuel pump 5 arranged between the low-pressure fuel pump and the fuel injection valves 1. Also illustrated are fuel filters 6,7 arranged in inlet parts of the fuel line, a check valve 8, a low-pressure control valve 9 as a low-pressure control unit, and a high-pressure control valve as a high-pressure control unit.
This fuel feeding system for an internal combustion engine is applied to an in-cylinder injection gasoline engine in which fuel is directly injected into cylinders. As is illustrated in FIG. 5, the fuel line 3 is composed of a feed line 3A for feeding fuel from the fuel tank 2 to the injectors 1 and a return line 3B for returning fuel, which has not been injected through the injectors 1, to the fuel tank 2. Further, the injectors 1 are fed with fuel through a delivery pipe 1A. This delivery pipe 1A itself shall also be considered herein as a part of the fuel line 3.
The low-pressure fuel pump 4 is an electrically-driven feed pump arranged in the feed line 3A of the fuel line 3 at an upstream location thereof within the fuel tank 2, and is actuated concurrently with a start-up of the engine and is stopped at the time of a stop of the engine. It can produce a predetermined delivery pressure irrespective of an engine speed, and pressurizes fuel from a level of atmospheric pressure to about several atmospheres or so.
The high-pressure fuel pump 5 serves to pressurize the fuel, which has been delivered from the low-pressure fuel pump 4, to several tens of atmospheres or so. As this high-pressure fuel pump 5, a pump of the engine-driven type (hereinafter called the "engine-driven pump") is used. Obviously, the high-pressure fuel pump operates in direct association with an operation of the engine and produces a delivery pressure in accordance with an engine speed.
Incidentally, the check valve 8 is interposed in the feed line 3A between the low-pressure-fuel pump 4 and the high-pressure fuel pump 5. By this check valve 8, the pressure of fuel delivered from the low-pressure fuel pump 4 is maintained.
Further, between the feed line 3A and the return line 3B of the fuel line 3, the low-pressure control valve (low-pressure regulator) 9 is arranged to regulate a delivery pressure from the low-pressure fuel pump 4 to a preset pressure (for example, 0.33 MPa, namely, about 3 atm or so).
At a location immediately downstream of the injectors 1, a high-pressure control valve (high-pressure regulator) 10 is disposed to regulate a delivery pressure from the high-pressure fuel pump 5 to a preset pressure (for example, 5 MPa, namely, 50 atmospheres or so).
A bypass passage (hereinafter called the "first bypass passage") 11 is arranged bypassing the high-pressure fuel pump 5. In this first bypass passage 11, a check valve 12 is disposed to permit passage of fuel only from an upstream side to a downstream side of the feed line 3A. This check valve 12 opens the first bypass passage 11 when the high-pressure fuel pump 5 does not operate fully, and closes the first bypass passage 11 when the high-pressure fuel pump 5 operates fully.
In addition, a bypass passage (hereinafter called the "second bypass passage") 13 is arranged bypassing the high-pressure control valve 10. This bypass passage 13 is provided with a solenoid-operated directional control valve (fuel pressure control valve) 14. This solenoid-operated directional control valve 14 opens at the time of a start-up of the engine, and remains closed after the start-up.
At a location immediately downstream of the solenoid-operated directional control valve 14, an orifice 15 is arranged so that, even when the return line 3B is still open shortly after a start-up of the engine, a fuel pressure close to a preset pressure controlled by the low-pressure control valve 8 can be obtained. This second bypass passage 13 enables a discharge of vapor (vapor bubbles), which are contained in the fuel line 3 around the injectors 1, in an initial stage of a start-up of the engine.
A controller 30 then controls the solenoid-operated directional control valve 14 so that the solenoid-operated directional control valve 14 is energized and opened at the time of a start-up operation and is deenergized and closed in a normal operation state.
At the time of a start-up operation, an injector gain and an injector dead time are also set on low pressure sides.
Owing to the constitution as described above, control of a fuel supply can be performed, for example, as shown in FIG. 6.
First, it is determined whether or not the engine is in a stalled state (step S401). If it is not in a stalled state, it is then determined whether or not an ignition key switch 16 has been turned to a starter-on position (step S402). If the ignition key switch 16 has been turned to the starter-on position, a start-up operation mode is set and a timer is reset to 0 (step S403).
In this case, concurrently with a start-up (namely, cranking) of the engine, the low-pressure fuel pump 4 and the high-pressure fuel pump 5 are actuated and at the same time, the controller 30 energizes the solenoid-operated directional control valve 14 to open the second bypass passage 13 (step 404) and also drives the fuel injection valves 1 under control in a particular operation mode. Namely, an injector gain for a low pressure mode is selected (step S405) and an injector dead time for the low pressure mode is selected (step S406).
Then, if an engine speed is determined to be in excess of a predetermined value (for example, 430 rpm), the start-up mode is determined to have ended. The routine thus advances from step S402 to step S407, where it is determined whether or not an engine speed has exceeded a first reference speed (for example, 1,000 rpm). If the engine speed is determined to be in excess of the first reference speed (1,000 rpm), the timer starts counting (step S408).
A determination in step S409 is then performed, that is, it is determined whether or not a count of the timer has reached a predetermined value. If the count of the timer has not reached the predetermined value, the routine advances to step S410 to determine whether or not the engine speed has exceeded a second reference speed (for example, 2,000 rpm).
If the engine speed has not exceeded the second reference speed (2,000 rpm), the operations of steps S404-S406 are continued until a count of the timer reaches the predetermined value (namely, until a predetermined time has elapsed).
In this state, the fuel--which has been delivered from the low-pressure fuel pump (feel pump) 4 and then regulated to a predetermined low pressure value through the downstream low-pressure control valve (low-pressure regulator) 9--is supplied to the fuel injection valves (injectors) 1 and any surplus portion of the fuel is returned to the fuel tank. The low-pressure fuel pump 4 is promptly brought to a delivery pressure level of a predetermined pressure (several atmospheres) subsequent to a start-up. Shortly after the start-up of the engine, however, the engine speed does not increase so that the high-pressure fuel pump 5 cannot produce a sufficient delivery pressure.
Shortly after the start-up of the engine, the high-pressure fuel pump 5 therefore rather acts as a resistance to the passage of a flow of the fuel through the fuel line 3 under the delivery pressure from the low-pressure fuel pump 4. In this system, however, the fuel is supplied toward the fuel injection valves 1 through the first bypass passage 11 arranged in parallel with the high-pressure fuel pump 5. From the fuel injection valves 1, a fuel injection can therefore be performed at a fuel pressure similar to a pressure regulated by the low-pressure control valve 9.
Shortly after a start-up of an engine, a quantity of fuel required for combustion is generally small so that a pulse width for fuel injection is short. Further, a pulse timing for the fuel injection is sufficient if it takes place only in an intake stroke as in the conventional multipoint injection (MPI). As the injector gain and injector dead time for the low pressure mode are selected accordingly and the fuel injection is then performed, the engine speed can be smoothly increased even at a fuel pressure similar to the level of the pressure regulated by the low-pressure control valve 9 insofar as the fuel pressure is stable.
As a consequence, with an increase in the engine speed, the delivery rate of the high-pressure fuel pump 5 progressively increases and the delivery pressure of the high-pressure fuel pump 5 also increases smoothly. When the engine speed has exceeded the second reference speed (2,000 rpm), or when a predetermined time has elapsed with an engine speed in excess of the first reference speed (1,000 rpm) but not higher than the second reference speed (2,000 rpm), the routine advances from step S409 or step S410 to step S411 and the controller 30 closes the solenoid-operated directional control valve 14 to drive the fuel injection valves 1 under control in a normal operation mode (namely, the high pressure mode). Namely, an injector gain for the high pressure mode is selected (step S412), and an injector dead time for the high pressure mode is selected (step S413). Then, the timer is reset to 0 (step S414). After that, the operations of steps S411-S414 are continued for as long as the engine does not stop.
As a result, the fuel is delivered from the low-pressure fuel pump (feed pump) 4 and is then pressurized to a high pressure through the high-pressure fuel pump 12. Further, the fuel which has been regulated to a predetermined high pressure value by the high-pressure control valve (high-pressure regulator) 10 is supplied to the fuel injection valves (injectors) 1 and any surplus portion of the fuel is returned to the fuel tank.
Accordingly, the delivery pressure of the high-pressure fuel pump 5 progressively increases the fuel pressure on the downstream side of the high-pressure fuel pump 5 without being lost, whereby the fuel pressure is raised to or beyond the pressure regulated by the high-pressure control valve 10. Further, owing to the selection of the injector gain for the high pressure mode and the injector dead time for the high pressure mode, fuel injection can be performed adequately.
The delivery pressure of the high-pressure fuel pump 5 rises to a sufficient level as described above, thereby making it possible to perform fuel injection from the fuel injection valves 1 at a high fuel pressure similar to the pressure regulated by the high-pressure control valve 10. The engine speed is therefore smoothly increased from shortly after a start-up of the engine. It is therefore possible to obtain a high fuel injection pressure, which is required for shortening the fuel injection duration (namely, the pulse width for fuel injection) or is required corresponding to a supercharging pressure during supercharging, for example, in an in-cylinder injection internal combustion engine.
Further, the solenoid-operated directional control valve 14 which serves to open or close the second bypass passage 13 is closed after the predetermined time (a relatively short time) has elapsed and a discharge of vapor has been fully effected. Then, it is therefore possible to raise the fuel pressure to a pressure regulated by the high-pressure control valve 10, thereby making it possible to obtain a sufficient fuel injection pressure, for example, during a high speed operation or the like.
Incidentally, according to the above-described conventional art (see FIG. 5 and FIG. 6), a specific operation state is set, the solenoid-operated directional control valve 14 is opened, and upon start-up, a flow passage is secured on the downstream side of the injectors 1 for the fuel delivered from the low-pressure fuel pump 4. The fuel is therefore allowed to stably flow at a low pressure. With this fuel flow, vapor (vapor bubbles) which are contained in the fuel line 3 around the injectors 1 are discharged in an initial stage of a start-up of the engine.
Nonetheless, a situation is conceivable where the solenoid-operated directional control valve 14 may become not fully operative or inoperative due to a disconnection, sticking of the solenoid-operated directional control valve 14 or the like. As the solenoid-operated directional control valve 14 is set in a closed position under the force of a spring while no electricity is supplied, the second bypass passage 13 remains closed in such a situation, that is, upon occurrence of a disconnection or sticking of the solenoid-operated directional control valve 14, so that the fuel pressure cannot be controlled to a low pressure. However, when a drive signal is delivered to the solenoid-operated directional control valve 14, a signal is concurrently sent to the injectors to control their drive duration to a fuel injection valve drive duration corresponding to a low fuel pressure (i.e., a duration longer than that for a high pressure time). Although the fuel pressure has arisen actually, the injectors are therefore actuated corresponding to a pressure lower than the fuel pressure. The fuel is hence not injected in an appropriate quantity, leading to a problem that the engine is deteriorated in start-up performance and in worst cases, may become no longer feasible to perform a start-up.
With the foregoing problem in view, the present invention has been completed. An object of the present invention is therefore to provide a fuel feeding system for an internal combustion engine, which makes it possible to perform good combustion in the engine even when a fuel pressure determination unit such as a fuel pressure control valve becomes inoperative.